1. Field of the Invention
The present invention relates to a charging technique to charge a body to be charged, and particularly to a technique to contribute to the improvement of charging efficiency.
2. Description of the Related Art
Hitherto, as a charging system or a transfer system used for an image forming apparatus such as an electrophotographic apparatus, a corona charging device is often used mainly as a non-contact charging system. In addition to this, as a non-contact charging system with less ozone generation, there is known roller charging, brush charging, blade charging, magnetic brush charging, proximate charging to charge a charging device, such as a roller, through a gap of several μm to several hundred μm relative to a member to be charged, such as a photoconductor, or the like.
In the case where the roller charging or the proximate charging is used, although the amount of ozone generated from the used equipment can be reduced to a safety level, there is a problem that an electric discharge occurs at close distance from a photoconductor, high-density ozone is generated, and ion impact by an intense electric field is given to the photoconductor, and accordingly, the life of the photoconductor is remarkably shortened. This is a problem from the viewpoint of resource saving, and this is a problem that safety is not ensured.
On the other hand, in the magnetic brush charging device, a magnetic roller is used as a charging roller, a carrier particle as in general two-component magnetic brush development is attached to the charging roller by magnetic force to form a magnetic brush, and the magnetic brush is brought into contact with the surface of a body to be charged, such as a photoconductor, to charge it. At this time, the resistance of the carrier particle and the surface resistance at the photoconductor side are adjusted, so that the efficient charging becomes possible by an electric charge injection phenomenon without electric discharge, and the charging at low bias and without ozone generation becomes possible (see, for example, JP-A-8-339113, JP-A-2001-51480).
However, in the magnetic brush charging, as described above, in addition to the characteristics of the carrier, unless the resistance of the surface of the photoconductor is made low, satisfactory injection charging can not be performed, and accordingly, when a surface layer with low resistance or the like is used for the photoconductor, there have been disadvantages that when a high-definition image is tried to be formed, the image is blurred or becomes foggy.